Science is a process, not merely a collecting of bits of information. To that end, one of the most rewarding things that comes from being involved in science is not just the discovering of new stuff, but the seeing of how ideas and proposals are received over the years, how they weather the accruing of new data, how they’re incorporated into developing models, and even how and why they’re not incorporated into said models. Needless to say, all of this is especially interesting when the data itself is your own: whether it’s a lone data point, a stack of data, or a theoretical model, it’s normal (I think… I hope) to see that stuff as ‘your baby’ and to care about what happens to it.

The Xenoposeidon type specimen, as illustrated by Taylor & Naish (2007), in (A) left lateral, (B) right lateral, (C) anterior and (D) posterior views. It’s a weird vertebra indeed, the forward-sloping neural arch being just one of many weird details. Credit: Taylor & Naish 2007

On November 15th 2007, sauropod expert Mike P. Taylor and myself published Xenoposeidon proneneukos, a sauropod from the Lower Cretaceous rocks of East Sussex, England, based on the single dorsal vertebra NHMUK R2095 (held in the collections of The Natural History Museum, London). The big deal about Xenoposeidon is not just that we named it as a new taxon, but that we found it to be so weird compared to other sauropods that – we thought – it might represent some new, hitherto unrecognised, sauropod lineage. That’s a bold claim to make on the basis of a single bone, but science is all about going where the evidence leads. Anyway, Mike and I both had a lot of fun with the publicity surrounding our original paper (Taylor & Naish 2007), and a ton has been written about Xenoposeidon online, mostly at the sauropod-themed blog SV-POW!The original, 2007 Tet Zoo take on the specimen is here.

Here’s one of several ‘full-body reconstructions’ of Xenoposeidon we had made: this one shows Xeno in position on Matt Wedel’s brachiosaur reconstruction. In case anyone doubts, this was never meant to be remotely serious. And Xeno is not thought to have been brachiosaur-shaped anymore, anyway. Credit: Mike Taylor (CC BY 4.0)

So, here we are, ten years on. I wasn’t able to publish anything on the 10th birthday itself, but I figure today is close enough – it’s the right month, at least. What has happened to our beloved Xenoposeidon in those ten intervening years? Oh, and belated happy birthday, Xeno.

Wow, Xeno gets mentioned in a book within just a year of its description, not bad. Oh sure, I wrote the book in question but that’s coincidental. Credit: Darren Naish

The good news is that Xenoposeidon has hardly been ignored. That would be embarrassing. It has, I’m pleased to say, been incorporated into reviews, been given appropriate critique, been mentioned in books, and been listed – where appropriate – as a member of its respective faunal assemblage. Remember that one way of dealing with problematic nonsense in the technical literature (not to mention anyone in particular...) is simply to ignore it outright, so: so far so good. Naturally, some mentions of Xenoposeidon are but mere allusions to its existence (Taylor 2009, Naish 2010, Taylor et al. 2011, Upchurch et al. 2015, Royo-Torres et al. 2012, 2017). Even by 2009, Xenoposeidon was considered famous enough to warrant mention in a popular book… ok, I wrote that book (Naish 2009), but you see where I’m coming from. Anyway, what about more extensive stuff?

Xenoposeidon’s first decent outing was that provided in Mannion & Upchurch’s (2010) paper on the completeness of the sauropod fossil record: they used it as an example of a taxon named for extremely fragmentary material and also to illustrate the uneven distribution of phylogenetically informative character states across taxa. Xenoposeidon was, Mannion & Upchurch (2010) noted, described as possessing six diagnostic characters (Taylor & Naish 2007). This is more than (or the same as) that said to be present in Barosaurus and Omeisaurus, two sauropods known from substantially better material, to put it mildly. The point there is that evaluations of taxa are hardly created equal; I somehow doubt that Xenoposeidon is really that much ‘more diagnosable’ than is Barosaurus or Omeisaurus.

Xeno is in another book - and this time it gets a full evaluation. Truly we have struck the big time now. Credit: Darren Naish

In their re-evaluation of the Argentinean andesauroid Andesaurus, Mannion & Calvo (2011) made some anatomical comparisons with Xenoposeidon, and noted that the latter might turn out to be a weird, early-diverging titanosaur (an idea mooted in our original paper but ultimately not favoured). A long critique of the taxon – useful proof that it was definitely being taken seriously by other sauropod workers – was included in Upchurch et al.’s (2011) review of Wealden sauropods (for more on the volume concerned, the Tet Zoo take is here). While being conservative overall as goes which Wealden sauropods they were prepared to accept as valid, Upchurch et al. (2011) agreed with us that Xenoposeidon was likely valid, but felt it most likely that it was an early-diverging member of Somphospondyli, the sauropod clade that includes andesauroids, euhelopodids and titanosaurs.

Another evaluation was provided by D’Emic (2012) who, in contrast to previous appraisals, argued that Xenoposeidon was likely not valid since the features we described were either errors of interpretation, or present in other sauropods. So, a challenge. Has this been responded to? Yes: read on. And another evaluation was published by Mannion et al. (2013). They noted the weird mix of characters present in the specimen and the problems with all previous ideas on its phylogenetic placement. They suggested an unresolved position within Macronaria (the sauropod clade that includes Camarasaurus, brachiosaurids and somphospondylans).

The 50% majority rule consensus tree from Taylor & Naish (2007). We preferred, at the time, the identification of Xenoposeidon as a neosauropod of uncertain position, but this tree recovered Xeno as a member of the macronarian clade Titanosauriformes. Credit: Taylor & Naish 2007

And this brings us up to the present, since recent weeks have seen the publication of another study dedicated to Xenoposeidon: Taylor (2017), an open access paper (as yet, a preprint and not peer-reviewed) that both restates the validity of Xenoposeidon, and argues for a placement within the diplodocoid clade Rebbachisauridae. As Mike explains therein, Xenoposeidon shares a weird, ‘M’-shaped arrangement of bony laminae on the side of its neural arch with the rebbachisaurid Rebbachisaurus, something he only noticed after Wilson & Allain (2015) published their rotating digital model of a vertebra belonging to this taxon. Mike also responded to D’Emic’s argument that Xenoposeidon is not valid: I’m not about to provide all the details (see the paper), but he disagreed.

At left, our original reconstruction and interpretation of Xenoposeidon (from Taylor & Naish 2007). At right, Mike Taylor's new interpretation of the specimen as a rebbachisaurid dorsal. This necessitates the reinterpretation of various of the laminae and other structures. Credit: Taylor & Naish 2007 (left); Mike Taylor (CC BY 4.0)(right)

So, Xenoposeidon is a rebbachisaurid? That’s an interesting idea that’s been kicking around for a while (Mike first mentioned it back in 2015), and it certainly looks plausible based on the new data concerned (Taylor 2017). Rebbachisaurids have become increasingly well known in recent years due to the discovery and description of new material from Africa, South America and Europe. In the light of this material – much of which is really good (meaning: well preserved and highly informative) – a reinterpretation of a single busted vertebra is not that significant. But, as a rebbachisaurid, Xenoposeidon might still be important because it seems to be from rocks dated to the lower Berriasian, this making it about 10 million years older than the next oldest rebbachisaurid (Histriasaurus from Croatia). This view – that Xenoposeidon comes from rocks of that particular age – might be due for revision, but that’s an issue I can’t discuss further right now (it has relevance to a whole bunch of Wealden taxa).

If you’re in need of some geographical and stratigraphic context, here are the maps and strat diagrams, respectively, from Taylor & Naish (2007). The terminology for the Wealden has been modified since the strat diagram was produced: the ‘Hastings Beds Group’ is now the Hastings Group, and the ‘Ashdown Beds Formation’ is now the Ashdown Formation. Credit: Taylor & Naish 2007

After ten long, happy years, Xenoposeidon has fared pretty well. It’s been mentioned in at least 14 technical papers (and probably more), has made appearances in at least three books, has been critically evaluated on at least three occasions subsequent to its original publication, and has now been the subject of one substantial, well-illustrated revision (albeit by the first author of its original description). This is pretty good going, and I suspect this puts it on par with taxa known from far more substantial remains. Do all dinosaurs named from scrappy remains get such treatment? Or is it that Xenoposeidon has proved especially intriguing and appealing as a subject worthy of comment? We will revisit this topic in a little while.

I mentioned that we had a lot of fun in promoting the 2007 Xeno paper, right? At left, a spoof 'Taylor Lab' poster produced by our friend and colleague, Matt Wedel. At right: Taylor and Naish with t-shirts, a mug and a wall-mounted print. This is how heroes live. Credit: Matt Wedel (left); Taylor and Naish (CC BY 4.0) (right)

ABOUT THE AUTHOR(S)

Darren Naish

Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com!

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